Calcium phosphates constitute the mineral part of bone tissue in mammals. There are different types of calcium phosphate:
- Tricalcium phosphate (a and b)
The chemical properties of calcium phosphates, including their behaviour in water, are directly related to their composition, in other words their Ca/P molar ratio.
The most widely used calcium phosphates are hydroxyapatite and tricalcium phosphate.
Hydroxyapatite HAP (Ca10 (PO4)6 (OH)2) and tricalcium phosphate TCP (Ca3(PO4)2) are obtained by aqueous precipitation of calcium nitrate, ammonium hydrogen phosphate with an ammonia solution. This synthesis produces a pasty material which is then filtered and dried to obtain a powder. For the preparation of HAP, the Ca/P molar ratio of the reagents is 1.67, while for the preparation of TCP, the molar ratio is 1.5.
The ceramics are formed using traditional processes, then sintered between 1,000°C and 1,300°C.
HAP and TCP are mainly used for their biocompatibility. HAP is the least soluble and least resorbable, whereas TCP is osteoconductive (used as a support for bone repair then gradually disappears by resorption).
Two-phase HAP/TCP materials have been developed for preparing materials with controlled bone resorption and replacement.
Hydroxyapatite and tricalcium phosphate are used exclusively in the biomedical sector and more specifically in the field of implantology, such as coatings on metal orthopaedic implants and also as bone fillers, bone substitutes and orthopaedic adhesives.